Experimental And Numerical Study On Unregulated Emissions From DME Engines

With the energy crises and environment issues being more intensive, people pay more and more attention to the research of alternative fuels and combustion styles of engines. As a clean and oxygen-containing fuel, DME (Dimethyl Ether) has been considered one of the most attractive fuels for compression ignition engines due to the broad resources of its feedstocks and excellent performance of economy and emissions, DME engines are considered to be an important solution to China's energy security and environmental protection.Based on a wide reading and detailed study of relevant references, this thesis at first summarizes the current research, existent problems and developmental direction of DME engines. The test beds of DME DI and HCCI engines were modified and established on a 195 prototype diesel engine. By changing the injection starting pressure, fuel injection timing, nozzle position, spray orifice diameter, intake temperature, compression ratio and the clearance around the piston, the experimental study on engine's performance of combustion and exhaust emissions were carried out. With the use of Gas Chromatography and Fourier Transform Infrared Spectrometry, some unregulated emissions such as formaldehyde, formic acid and methyl formate from the DME fueled engines are specially analyzed.In view of the limitation of multi-dimensional simulation in PC capacity, a reduced chemical reaction model is presented, which contains 33 species and 76 elementary reactions. The calculated results show that, this reduced model is valid in simulating HCCI engine operations in a wide range of initial conditions. It also can predict the species concentration profiles such as formaldehyde, formic acid and methyl formate.Coupling the above reduced model with a CFD software, a two-dimensional model is built to simulate the combustion and pollutants formation of DME HCCI engines. The influences of parameters, such as intake temperature, intake pressure, equivalence ratio, compression ratio and the clearance around the piston, are calculated and validated to the engine performances. The variation history of the in-cylinder species concentrations are also predicted and analyzed.